Originally posted by Bass Mechanic
ummm NO! your compleatly wrong about that statement.
a ported box goes considerably lower than a sealed box and has far less cone travel than a sealed box. also has less distortion because of less cone movement and has more SPL than a sealed box because of the added area of the port.
here is a responce graph that has a JL audio sub as an example. notice that the sealed box has an F3 of 50 hz while the ported box has an F3 of 34hz if my math is correct i belive the ported box has considerably lower frequency responce than the sealed box. it also has a gain of 3db over the sealed box over about 75% of the usable frequencies.
if i showed you an incar responce (and i can) of this example you would find that the ported box maintains the SPL at 35 hz with a 5-6db gain over the sealed box.
also the point of porting a box is not to tune it to some off the wall frequency. you pick a frequency that compliments the woofer and the box. as you can see in this example the tuning frequency is at 29.31hz but it still has more output and less cone travel than the sealed box until it comes to about 22 hz. this is where a subsonic filter is used to prevent the cone from getting excessive travel. also notice that the cone travel does not even reach the xmax limit until 20 hz. there is still mechanical limit available below 20hz.
unless you plan to listen to elephant calls in the sub 20hz zone there is really no need for a subsonic filter in this example. most all music does not contain program material that falls below 20 hz. a subsonic filter is good added protection but not a requirement if you design the box correctly.
Ok, I think we got the definition of LOW and LOUD mixed up here. A ported box is a helluva lot louder than a sealed, thats for sure. However, it does not go lower as your own graph demonstrates. Look at the falloff on your ported box vs. sealed. The sealed box clearly goes lower, but the ported box is louder above 20Hz. And look at the cone displacement graph. There's no way that ported sub is producing a clear sound below 20 Hz. I realize that 20 Hz is not used much, but I am just saying that a sealed box will produce it much more clearly than ported, which means it is capable of a lower frequency response. Every sub manufacturer I've ever seen says this in their manuals. I may have been wrong by saying a ported box can't go below the tuning frequency, but I am not wrong in saying that a sealed will go lower without distortion.
For SQ, you want a smooth response, which the ported box simply does not give as well as the sealed. if the opposite was true then a sealed box would never be used for SQ, which it almost always is.
just a little FYI.. i have been building boxes for over 15 years. and have recently designed a subwoofer box that has broken all the rules for what typically you expect from different types of boxes.
usually a sealed box is the tight accurate box design, ported are known for extended LOW frequency responce and bandpass boxes are known for good SPL but not so good of SQ.
my computer designed subwoofers and computer designed bandpass boxes have combined all 3 aspects into one box. the box happens to be a bandpass but if you ask anyone that has heard it they will all tell you the same thing.. it is simply awesome!
i belive there is are 2 members on this board that will attest to that fact.
thanks for your time.
Kevin
Indeed. Perhaps you can do some things to those boxes you are designing to mess with the physics, many people do that, but all things being equal with boxes built to manufacturers spec, sealed boxes have a better low end (sub 20Hz) response than ported, they are better for SQ because of the smoothness of the response curve, however are not as efficient as ported boxes.
I have ported and would never look back. At least not with my 12L7, that thing is great ported.
-Diabolik